Many irrigation controllers have been developed for automatically controlling application of water to landscapes. Known irrigation controllers range from simple devices that control watering times based upon fixed schedules, to sophisticated devices that vary the watering schedules according to local geographic and climatic conditions.
With respect to the simpler types of irrigation controllers, a homeowner typically sets a watering schedule that involves specific run times and days for each of a plurality of stations, and the controller executes the same schedule regardless of the season or weather conditions. From time to time the homeowner may manually adjust the watering schedule, but such adjustments are usually only made a few times during the year, and are based upon the homeowner's perceptions rather than the actual watering needs. One change is often made in the late Spring when a portion of the yard becomes brown due to a lack of water. Another change is often made in the late Fall when the homeowner assumes that the vegetation does not require as much watering. These changes to the watering schedule are typically insufficient to achieve efficient watering.
More sophisticated irrigation controllers usually include some mechanism for automatically making adjustments to the irrigation run times to account for daily environmental variations. One common adjustment is based on soil moisture. It is common, for example, to place sensors locally in the soil, and suspend irrigation as long as the sensor detects moisture above a given threshold. Controllers of this type help to reduce over irrigating, but placement of the sensors is critical to successful operation.
More sophisticated irrigation controllers use evapotranspiration rates for determining the amount of water to be applied to a landscape. Evapotranspiration is the water lost by direct evaporation from the soil and plant and by transpiration from the plant surface. Potential evapotranspiration (ETo) can be calculated from meteorological data collected on-site, or from a similar site. One such system is discussed in U.S. Pat. No. 5,479,339 issued December, 1995, to Miller. Due to cost, most of the data for ETo calculations is gathered from off-site locations that are frequently operated by government agencies. Irrigation systems that use ETo data gathered from off-site locations are discussed in U.S. Pat. No. 5,023,787 issued June, 1991, and U.S. Pat. No. 5,229,937 issued July, 1993 both to Evelyn-Veere, U.S. Pat. No. 5,208,855, issued May, 1993, to Marian, U.S. Pat. No. 5,696,671, issued December, 1997, and U.S. Pat. No. 5,870,302, issued February, 1999, both to Oliver, U.S. Pat. No. 5,097,861 issued March 1992 to Hopkins, et al., and U.S. Pat. No. 6,102,061, issued August, 2000 to Addink. These and all other referenced patents are incorporated by reference herein.
Due to cost and/or complicated operating requirements very few of these efficient irrigation controllers, discussed in the previous paragraph, are presently being installed on residential and small commercial landscape sites. Therefore, controllers that provide only inadequate schedule modification are primarily used to irrigate most residential and small commercial landscape sites. This results in either too much or too little water being applied to the landscape, which in turn results in both inefficient use of water and unnecessary stress on the plants. Therefore, a need existed for a cost-effective irrigation system for residential and small commercial landscape sites that is capable of frequently varying the irrigation schedule based upon estimates of actual water requirements.
This need was met in part by a recent patent application, U.S. application Ser. No. PCT/US00/18705. The patent discusses operation of an irrigation controller comprising: a memory that stores a regression model; a microprocessor that applies a value for an environmental factor to the regression model to estimate an evapotranspiration rate (estimated ETo); and a mechanism that uses the estimated ETo to affect an irrigation schedule executed by the controller. Some of the environmental factors from which the value is obtained are temperature, solar radiation, wind speed, and humidity. Although, all four meteorological factors; temperature, solar radiation, wind speed, and humidity, are typically used in a formula for calculating the actual ETo, temperature and solar radiation have a greater effect on the ETo value than either wind speed or humidity. Therefore, if temperature and/or solar radiation were used for determining the estimated ETo this would provide a closer approximation to the actual ETo value than if either wind speed or humidity were used. An even closer approximation to the actual ETo value would be obtained if a combination of temperature and solar radiation were used for determining the estimated ETo. Pending patent application Ser. No. PCT/US00/18705 discusses using actual solar radiation to estimate ETo whereas the present patent uses estimated solar radiation to determine the estimated ETo
Temperature data for any given installation is typically obtained using only one type of sensor. However, solar radiation data can be obtained by various solar radiation measuring devices, all of which have the commonality of an optical port through which the solar radiation passes prior to being measured by some means. There is usually a diffuser or some other cover over the optical port, which can be of any suitable material that does not unduly interfere with the solar radiation reaching the measuring means. Unfortunately, this can be problematic since the cover must be kept clean to prevent foreign material from interfering with the solar radiation reaching the measuring means.
The solar radiation data obtained and used in the determination of ETo is generally obtained from government weather stations. Maintenance is done according to a regular schedule at most or all weather stations, and the solar radiation sensor diffuser or cover is cleaned during each of the scheduled maintenance visits. However, if solar radiation were to be used at a homeowners' residence to estimate ETo for irrigation purposes, the homeowner would probably not do the necessary maintenance to keep the optical port cover clean and the solar radiation data would not be very reliable. What is required is another method for estimating solar radiation that does not require regular maintenance, and would still provide a relatively close approximation of the actual solar radiation at the irrigation site.